Despite a century of technological advances, drilling and construction of oil and gas wells remains a slow, dangerous, and expensive process. The costs of some wells can exceed 100 million dollars. A significant contributor to these high costs is due to suspension of drilling in order to repair geologically-related problem sections in wells. These problems can include, but are not limited to, lost-circulation, borehole instability, and well-pressure control. However, these problems are still generally rectified only by costly and time-consuming casing and cementing operations. Such conventional stabilization and sealing processes are required at each problem-instance, often dictating installation of a series of several diametrically descending, or telescopic-casing strings. Generally, a casing string is installed from the surface to each problem zone and a 10,000 foot deep well often requires 20,000-30,000 feet of tubulars, because of overlapping sections.
As is well known in the art, disadvantages of telescoping practices are numerous. These disadvantages include, but are not limited to, excess excavation work, special equipment for over-size rock borings, and production of costly waste products. Beginning diameters in excess of 24 inches are usually required to allow a diameter of about 5 inches or less at the end of a final production string. Large-scale drilling operations can require drilling equipment hoist ratings as high as 2,000,000 pounds and may require several acres for the drill-site. Both requirements can be attributed to various casing needs and operations. Despite major expenditures and efforts, drilling might not reach the targeted resources. If the final telescope casing size (or production string) is too small to economically produce the hydrocarbon resource, the result is a failed well.
The energy industry, therefore, has pursued development of plastically-deformed expandable well-casings and single diameter well-casing systems (also known as “mono-diameter” or “monobore”), wherein one size casing is preferably used from the surface to the target zone, typically some 1-7 miles below. Single diameter concepts can replace former surface-to-problem-zone casing string installation, with discrete-zone placement of an expandable casing. For example, a median casing size of 9⅝ inch outside-diameter (“OD”) in an un-expanded state can be passed through a casing in the expanded state, and then the un-expanded casing can then be expanded to function in a nominal 10 inch to 12 inch borehole by means of a cold-work, mechanical steel deformation process performed in-situ. The expanded casing assembly must, however, meet certain strength requirements and allow passage of subsequent 9⅝ inch outer diameter casing strings as drilling deepens and new problem zones are encountered.
The foregoing deforming process inherently requires use of relatively soft steels, which may not provide the desired mechanical properties required in the environments of oil and gas wells. It is believed that most potential users cannot utilize current expandables due to fundamentally unsolvable technical or economic issues.
For example, it is believed that conventional expandable tubulars do not provide a good seal, because they do not comply adequately with the irregular wall surfaces of wells. Expandable tubulars made of steel materials have a natural tendency to “spring back” from their altered states to their natural or original form. Spring back is also sometimes referred to as “recovery”, “resilience”, “elastic recovery,” “elastic hysteresis,” and/or “dynamic creep.” Spring back exists in all stages of worked materials. For pre-ruptured tubes, different degrees of deformity throughout the thickness of the tube-arc can translate into spring back rates that vary according to the severity of arc resulting from the deformation. As a result, it is believed that conventional expandable tubulars can never properly comply or seal.
Furthermore, plastic deformation is achieved by forcing an expansion device, such as a pig or a mandrel to expand and permanently deform the tubular. The expansion device can be (1) forced downward through the tubular to deform it (2) pulled upward through the tubular, (3) rotated within the tubular, or (4) combinations thereof The expansion device can also have tapered wedges or rollers. However, it is also well known that high-levels of deformity can cause stress-cracking, a variety of metallurgical problems, and decreased mechanical properties.
A further disadvantage of presently known expandable tubulars is that as the tubular is deformed radially, such outward radial expansion causes the overall length of the tubular to be shortened by some 1% to 3% or more. Such shrinkage along the longitudinal axis of the tubular member is undesirable. An inability to supply extra material to the shrinkage can impede radial expansion. For example, if the pre-expanded casing becomes “stuck” or otherwise placed into tension longitudinally, the need to service the shrinkage cannot be met and the deforming material becomes prematurely strained. This is also a major source of difficulty when expanding threaded connections.